1. Field of the Invention
This invention relates to an anti-tumor agent containing protease originating from microorganisms as an effective component, to an anti-tumor agent containing chemically modified protease originating from microorganisms as an effective component, to a chemically modified protease originating from microorganisms and to a method of using such agents.
As a result of extensive studies to prepare anti-tumor agents with less side-effects on the basis of the long experiences of the inventors in the study of anti-tumor agents, the present inventors have found, for the first time, that protease originating from microorganisms, that is, a group of substances of quite a different category in the molecular properties and mechanism of action from those of the conventional anti-tumor agents, has quite effective anti-tumor action. As a result of further studies, the present inventors have also found that anti-tumor agents containing chemically modified proteases as effective components have much better anti-tumor effect than the parent proteases.
The action of proteases and chemically modified proteases originating from microorganisms as effective components of the present anti-tumor agent are degradation of proteins and the consequent cell rupture, and thus the present anti-tumor agents have an action of a quite different category from those of the conventional anti-tumor agents.
2. Related Background Art
The present inventors have already found that the structure of blood vessels in a tumor tissue is quite different from that in the normal tissue. Furthermore, lymphatics appears inoperative in the tumor tissue. That is reflected in the behavior of a high molecular weight anti-tumor agent when it is administered into the tumor tissue. Namely, its fate is quite different from that of a low molecular weight one; the high molecular weight substance is not recovered into the blood circulation nor cleared from the lymphatic system due to its absence, thus it is retained in the tumor tissue for a prolonged time. This seems due to the fact that the high molecular weight lowers the diffusion rate of the agent and also reduces the passage into the blood vessel and consequently permeation into the blood vessels and successive recovery efficiency are lowered. Furthermore, the present inventors have already found that solid tumor sites are lacking in lymphatic vessels, whereas in the normal tissue, the lymphatic system is the main route for recovery of high molecular weight and lipid substances and microparticles in such a tissue. A tumor tissue is lacking in such a lymphatic system as described above, and thus the high molecular weight substances such as enzymes, etc. can stay at the tumor site for a prolonged time [Iwai, K. et al. Cancer Res. 44, 2115-2121 (1984); Maeda, H. et al: J. Prot. Chem., 3, 181-193 (1984); Maeda, H. and Konno, T.: Gan to Kagaku Ryoho 12, 773-782 (1985); Maeda, H. et al: Protein Tailoring for Food and Medical Uses, 353-382 Feeney, R. E. and Whitaker, J. R. ed. Marcel Dekker Inc., N.Y. (1986)].
Taking these finding into account, the present inventors have presumed that when proteases and chemically modified proteases originating from microorganisms as high molecular weight substances are injected into the site, some of them could exhibit a powerful toxicity against tumor cells for a prolonged time and remarkable anti-tumor effect could be obtained.
The anti-tumor agents so far developed are mainly low molecular weight agents usually less than 2,000 dalton, which undergo rapid diffusion, and thus their pharmacological action in the tumor tissue cannot be maintained for a prolonged time unless their systemic concentration is maintained at a very high level even if they have a potent pharmacological action. This is a disadvantage and prime cause of severe side effects.